Patent GB-1013692-A (GB)
Title: Energization circuits for inductive devices
IPC: H03K17/042
Filed: 1961-12-18
Abstract: 1,013,692. Transistor switching circuits. TELETYPE CORPORATION. Dec. 18, 1961 [Jan. 3, 1961], No. 45241/61. Heading H3T. A circuit for supplying current to an inductor 31 comprises two transistors connected so that their emitter-collector paths are in series with the inductor across a source of voltage, one transistor 19, Fig. 1 (or 88, Fig. 2) serving as a switch and becoming saturated when an input pulse of suitable polarity is applied at terminal 23 and the other transistor 32 (or 69) also being switched on when an input pulse is applied to the circuit but being provided with an emitter resistor 39 (or 73, 74) and a fixed value of base bias voltage derived from a potential divider 37, 35 (or 81, 82) so that when the input pulse is first applied both transistors are saturated and a substantially constant voltage is maintained across inductor 31 and the current therethrough increases linearly until a predetermined value of current determined by the base bias and emitter resistor for the second transistor is reached whereupon the second transistor comes out of saturation and the current through the inductor is maintained at that predetermined value. In Fig. 1 the application of a positive-going input pulse causes transistors 11 and 12 to conduct, this being reinforced by regeneration through transistor 19 which thereby is also rendered conducting. Potential divider 37, 38 is thereupon energized to switch transistor 32 on and inductor 31 is consequently energized with a voltage substantially equal to that across resistor 37 which in its turn is a substantially constant proportion of the supply voltage, the effect of resistor 42 being negligible. Further regeneration from the remitter of transistor 32 via resistor 36 serves to ensure the maintenance of conduction in transistors 11 and 12. The current in inductor 31 increases linearly until the current reaches the maximum value which can be maintained by the fixed value of base bias voltage through emitter-resistor 39. The transistor 32 then comes out of saturation and the current in the inductor is thereafter maintained at said maximum value until the end of the input pulse. When the input pulse terminates, inductor 31 discharges through diode 40, resistor 42 and transistor 19. In Fig. 2, transistor 65 is initially conducting, all the other transistors being non-conducting. The application of a negative input pulse switches transistor 61 on so reducing the negative voltage at the base of transistor 65 and transferring conduction therefrom to transistor 69. Simultaneously the rise in negative voltage at the base of transistor 88 switches that transistor on so that inductor 31 becomes energized with a voltage substantially equal to that across resistor 82. The current in the inductor increases linearly until a predetermined value is reached whereafter it stays at that value for the remainder of the input pulse. The inductor is discharged through diode 87, resistor 83 and transistor 88. In this circuit regenerative loops are provided by transistors 61, 65 and resistor 73 and by transistors 65, 88, 69 and resistor 95.